共计 571 个字符，预计需要花费 2 分钟才能阅读完成。
Problem
Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.
Example:
Input: 38Output: 2 Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2.
Since 2 has only one digit, return it.
Follow up:Could you do it without any loop/recursion in O(1) runtime?
Solution 1
class Solution {
public int addDigits(int num) {
int sum = 0, cur = num;
if (num < 10) return num;
while (num >= 10) {
while (num >= 10) {
sum += num%10;
num /= 10;
}
sum += num;
if (sum >= 10) {
num = sum;
sum = 0;
} else return sum;
}
return sum;
}
}
Solution 2 – Mod 9
public class Solution {
public int addDigits(int num) {
if (num == 0){
return 0;
}
if (num % 9 == 0){
return 9;
}
else {
return num % 9;
}
}
}
